The objective of this project is to investigate in mammals the morphological and functional regenerative capacity of the vestibular nerve following surgical sectioning. Histopathological information will be obtained on (1) changes found in the vestibular nerve and the central nervous system projections of the regenerated primary afferents including the specificity of the projections of individual end-organ branches; (2) the time course of regeneration of fibers of different sizes, the rate of recovery of function and the correlation between anatomic regeneration and functional recovery; and (3) the role of vision n recovery of function of the regenerating nerve. A combination of classical histological techniques and the newest histochemical methods for studying the trajectory of nerve fibers, and computer based quantitative analysis will be used to document morphological changes. New electrophysiological methods for the study of vestibular reflex responses and evoked potentials will be utilized and the data analyzed with the aid of on-line computers. Evaluation and interpretation of data will be made in the context of models of vestibular function and rigorous statistical methods. This study will provide information that is relevant to basic science as well as clinical work. First, the ability to precisely test the functional capacity of the regenerated vestibular nerve makes this nerve an ideal model for studying the general problem of central nervous system regeneration. The clinical applications of this problem (CNS regeneration) are only now being realized. Second, physiological studies will provide additional information about central mechanisms of compensation of the vestibular system following peripheral injury. Finally, guidelines for sectioning of the vestibular nerve for relief of disabling vertigo must be developed if the vestibular nerve regenerates after surgical sectioning.